Ceramics and ceramic composites have been utilized as refractory materials in a number of different applications. It has been found that ceramic and ceramic composite refractories can be used as many different components for applications which require, among other things, good resistance to thermal shock, good corrosion, abrasion and erosion resistance, etc. For example, ceramic and ceramic composite materials have been utilized as liners in molten glass furnaces and molten metal furnaces, as well as in apparatus associated with such furnaces (e.g., apparatus which direct or constrict the flow of molten fluids from one point to another).
Exemplary uses for ceramic materials in molten metal furnace and molten metal transfer systems include furnace linings, slide gates, sub-entry nozzles, ladle shrouds, tundishes, etc. Many metal manufacturing processes (including steel manufacturing processes) have recently been changed from traditional batch processes to some type of continuous process for reasons of economy and productivity. However, these continuous processing methods place extreme requirements upon the materials which are in contact with the static or flowing molten materials. For example, in the steel industry, slide gate systems, which are used for controlling the flow of molten metal from a large chamber (e.g., a furnace) into a smaller chamber (e.g., a mold), have been known for many years. However, only recently certain materials have been manufactured to meet the necessary mechanical/physical requirements imposed by such systems. Generally, slide gate systems include some type of rotor design which consists of, for example, a fixed nozzle attached to and within a moveable plate. The flow of molten metal from a ladle is controlled by moving the moveable plate to fully or partially aligned openings. When filling the ladle, and during shut off, the openings are misaligned. The advantage which stems from the use of a slide gate in continuous metal casting is that the conventional stopper rod system is eliminated. Specifically, in conventional stopper rod systems difficulties were encountered in stopping and/or modulating molten metal flow through an opening. Often the conventional stopper rod systems were not completely successful in terminating the flow of molten metal therethrough. However, even though slide gate systems have been achieving great successes in improving continuous casting of molten metals, the stringent requirements placed upon the materials for use as slide gates have resulted in many problems for the material design engineer. Accordingly, the need for new and better materials continues.
To date, common materials for use in slide gate systems include tar-impregnated alumina materials, fired-magnesia materials, etc. However, these materials suffer from many material deficiencies such as, for example, certain metals may corrode the bonding media or matrix which is utilized to hold together the refractory. Additionally, conventional materials may not possess the desired combination of thermal shock resistance, corrosion resistance, erosion resistance, abrasion resistance, and/or strength which permit the materials to function for a sufficient amount of time to achieve the economies and efficiencies needed in modern manufacturing operations. Accordingly, a need exists to develop a material which exhibits corrosion resistance, erosion resistance, thermal shock resistance, abrasion resistance, sufficient strength, etc., to withstand the severe environment to which such materials are exposed in molten metals operations.
Similar corrosion, erosion, abrasion, thermal shock, etc., problems exist in the continuous manufacture of glasses. Specifically, glasses typically contain highly corrosive media (e.g., calcia, soda, magnesia, fluorides, chlorides, etc.) which may attack even the best ceramic materials. Moreover, glass producing operations also create severe thermal shock conditions as loll as highly erosive and abrasive conditions. Accordingly, the material engineer is also faced with difficult material design/fabrication problems in designing materials for use in the glass industry.
The present invention satisfies the above-discussed needs by providing materials which are useful in metal production and glass production industries. Specifically, the materials of the present invention can be used as refractories for direct contact with, for example, molten steel, molten aluminum, molten copper, molten bronze, molten iron, etc. Similar refractories can also be utilized for direct contact with molten glasses. Moreover, the refractory materials of the present invention have substantial erosion and abrasion resistance which permit, in many applications, the refractory materials to be in direct contact with each other and to be in sliding engagement with at least a portion of another surface of another refractory material (e.g., moveable parts of a slide gate for use in molten steel applications).